syzbot

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refcount_t: underflow; use-after-free.
WARNING: CPU: 3 PID: 10267 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 3 PID: 10267 Comm: syz-executor.0 Not tainted 6.10.0-rc5-syzkaller-00012-g626737a5791b #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 a8 e7 0e fd 84 db 0f 85 66 ff ff ff e8 fb ec 0e fd c6 05 1d c2 4c 0b 01 90 48 c7 c7 60 73 8f 8b e8 e7 6d d1 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 d8 ec 0e fd 0f b6 1d f8 c1 4c 0b 31
RSP: 0018:ffffc9000ca4fa48 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc90026129000
RDX: 0000000000040000 RSI: ffffffff81511296 RDI: 0000000000000001
RBP: ffffe8ffad27bd35 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: ffffe8ffad27bd35
R13: 0000000000000000 R14: 0000000000000002 R15: ffffe8ffad27bc51
FS:  0000000000000000(0000) GS:ffff88802c300000(0063) knlGS:00000000f5ea5b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f73de010 CR3: 00000000284ae000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:275 [inline]
 __refcount_dec_and_test include/linux/refcount.h:307 [inline]
 refcount_dec_and_test include/linux/refcount.h:325 [inline]
 skb_unref include/linux/skbuff.h:1224 [inline]
 __kfree_skb_reason net/core/skbuff.c:1195 [inline]
 kfree_skb_reason+0x1e8/0x210 net/core/skbuff.c:1222
 kfree_skb include/linux/skbuff.h:1257 [inline]
 flush_gro_hash net/core/dev.c:6683 [inline]
 __netif_napi_del net/core/dev.c:6698 [inline]
 __netif_napi_del+0x311/0x570 net/core/dev.c:6689
 gro_cells_destroy net/core/gro_cells.c:117 [inline]
 gro_cells_destroy+0x10a/0x4d0 net/core/gro_cells.c:106
 ip_tunnel_dev_free+0x19/0x60 net/ipv4/ip_tunnel.c:1100
 netdev_run_todo+0x775/0x1250 net/core/dev.c:10693
 setup_net+0x890/0xd60 net/core/net_namespace.c:371
 copy_net_ns+0x4ae/0x880 net/core/net_namespace.c:508
 create_new_namespaces+0x3ea/0xb10 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0xc0/0x1f0 kernel/nsproxy.c:228
 ksys_unshare+0x419/0x970 kernel/fork.c:3323
 __do_sys_unshare kernel/fork.c:3394 [inline]
 __se_sys_unshare kernel/fork.c:3392 [inline]
 __ia32_sys_unshare+0x30/0x40 kernel/fork.c:3392
 do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
 __do_fast_syscall_32+0x73/0x120 arch/x86/entry/common.c:386
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/common.c:411
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf72b3579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f5ea55ac EFLAGS: 00000292 ORIG_RAX: 0000000000000136
RAX: ffffffffffffffda RBX: 0000000068060200 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	10 06                	adc    %al,(%rsi)
   2:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
   6:	10 07                	adc    %al,(%rdi)
   8:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
   c:	10 08                	adc    %cl,(%rax)
   e:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1e:	00 51 52             	add    %dl,0x52(%rcx)
  21:	55                   	push   %rbp
  22:	89 e5                	mov    %esp,%ebp
  24:	0f 34                	sysenter
  26:	cd 80                	int    $0x80
* 28:	5d                   	pop    %rbp <-- trapping instruction
  29:	5a                   	pop    %rdx
  2a:	59                   	pop    %rcx
  2b:	c3                   	ret
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
  37:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi